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How to measure countersink angles of countersunk holes in sheet metal panels

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countersink angle, countersunk hole, sheet metal
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  #1  
Old 27th June 2006, 12:21 PM
RCW's Avatar
RCW

 
 
Posts: 434
Question How to measure countersink angles of countersunk holes in sheet metal panels

I am trying to measure the countersink angle of countersunk holes in sheet metal panels. I was told this could be done by using ball gages, placing several balls in the countersink, measuring their height off the panel, then by "using trigonometry, just calculate the angle."

Has anyone done this before? If so can you provide better instructions than what is listed above and/or the proper trig formula to use? Is there a better/easier way to measure the countersink angle? (I was looking into handheld gages to do this but they approximately $1000 each and have to be made for a specific diameter hole.)


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  #2  
Old 27th June 2006, 12:51 PM
Jim Wynne's Avatar
Jim Wynne

 
 
Posts: 14,077
Re: How to measure countersink angles

Quote:
In Reply to Parent Post by RCW

I am trying to measure the countersink angle of countersunk holes in sheet metal panels. I was told this could be done by using ball gages, placing several balls in the countersink, measuring their height off the panel, then by "using trigonometry, just calculate the angle."

Has anyone done this before? If so can you provide better instructions than what is listed above and/or the proper trig formula to use? Is there a better/easier way to measure the countersink angle? (I was looking into handheld gages to do this but they approximately $1000 each and have to be made for a specific diameter hole.)

A couple of thoughts:
  • Chamfer/c'sink gages don't have to be that expensive; look here for example. (No specific recommendation implied, just a < $1000 example).
  • In general, precision measurement of c'sink angles is a waste of time, especially if the purpose is to fit the head of a standard fastener. Put a screw in and see if it fits like it should, and you're done. Also, if the c'sinking is a captive operation (i.e., done where the inspection is done), you can just verify the tool used to make the c'sink. If it's the proper angle, the angle isn't going to be an issue. C'sink depth is more often an issue, as clueless engineers specify c'sink diameters that are too large for the material thickness, resulting in the hole at the bottom of the c'sink being enlarged beyond its UTL.
Thanks to Jim Wynne for your informative Post and/or Attachment!
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  #3  
Old 27th June 2006, 02:38 PM
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RCW

 
 
Posts: 434
Re: How to measure countersink angles

Quote:
In Reply to Parent Post by Jim Wynne

A couple of thoughts:
  • Chamfer/c'sink gages don't have to be that expensive; look here for example. (No specific recommendation implied, just a < $1000 example).
I already looked into these types of gages and will probably be purchasing one. However these gages only measure the outer diameter of the countersink and not the angle.

Quote:
In Reply to Parent Post by Jim Wynne

  • In general, precision measurement of c'sink angles is a waste of time, especially if the purpose is to fit the head of a standard fastener. Put a screw in and see if it fits like it should, and you're done.
A noble thought but when my customer comes in to look at my FAI data.....

My main purpose is to obtain equipment for data measurement & recording purposes. That and to keep my suppliers honest.

Quote:
In Reply to Parent Post by Jim Wynne

  • Also, if the c'sinking is a captive operation (i.e., done where the inspection is done), you can just verify the tool used to make the c'sink. If it's the proper angle, the angle isn't going to be an issue.
The items under inspection are from my suppliers so I don't have access to their tooling.

Quote:
In Reply to Parent Post by Jim Wynne

  • C'sink depth is more often an issue, as clueless engineers specify c'sink diameters that are too large for the material thickness, resulting in the hole at the bottom of the c'sink being enlarged beyond its UTL.
HIGHLY AGREED WITH!! I've seen countersunk holes that were approaching the diameter of the thru-hole. I've also inspected 2 identical pieces from the same lot and you can visually see a difference with the countersunk holes between the two units.
  #4  
Old 27th June 2006, 02:44 PM
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Jim Wynne

 
 
Posts: 14,077
Re: How to measure countersink angles

Quote:
In Reply to Parent Post by RCW

A noble thought but when my customer comes in to look at my FAI data.....

My main purpose is to obtain equipment for data measurement & recording purposes. That and to keep my suppliers honest.
My experience has been that telling customers that a verification like this doesn't add value is usually all that it takes. In most cases I've seen, they would rather see it verified with a screw. There are ways, of course, such as using a mold material, but it's messy and takes a while, and there's that ROI thing again. You can also keep your suppliers honest by using a screw. If the specification is for a 100-degree c'sink and they make 90s, you'll be able to tell in an instant, and hit your supplier over the head with incontrovertible evidence. Of course, it's best to avoid dishonest suppliers in the first place...
  #5  
Old 27th June 2006, 02:48 PM
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Jim Wynne

 
 
Posts: 14,077
Re: How to measure countersink angles

One more thing...there's also often an issue with the block tolerance for angles (typically +/- 1 degree) and measurement of c'sinks. If a c'sink is specified at 100 degrees and the proper tool is used, it's never going to be 103 or 97. There is no point in compiling variable data, in other words, unless your supplier is scooping them out with spoon.
  #6  
Old 27th June 2006, 02:56 PM
wweng7

 
 
Posts: 62
Re: How to measure countersink angles of countersunk holes in sheet metal panels

Measuring angle of c'sk tool is OK as long as you do not have build-up on tool itself. If you need to inspect actual angle of c'sk on the panel you can make a mold and check angle on comparator.
  #7  
Old 27th June 2006, 03:37 PM
Claes Gefvenberg's Avatar
Claes Gefvenberg

 
 
Posts: 4,839
Lightbulb Re: How to measure countersink angles of countersunk holes in sheet metal panels

Quote:
In Reply to Parent Post by RCW

Has anyone done this before?
I have not used that particular method but the enclosed drawing shows how to find the triangle you need. The rest, as your friend said, is trigonometry...sin x = (r1-r2)/height diff. Ordinary bearing balls can be used, no need for an expensive gauge.

/Claes
Attached Thumbnails
countersink.jpg  
Thanks to Claes Gefvenberg for your informative Post and/or Attachment!
  #8  
Old 28th June 2006, 08:14 AM
andygr's Avatar
andygr

 
 
Posts: 434
Re: How to measure countersink angles of countersunk holes in sheet metal panels

The use of the hight differance between ball of known sizes works well for angle actuals. An additional option is to cast the countersink and use an optical comparitator to measure the replication.
Inspection of this feature on an on going basis should be concentrated on the set up. The countersink angle changes as the cutter wears. Once you verify the actual dimension to address recording actual values for an as9102 FAI then move to process control. Check the first and last and all inbetween should be good. Key features are the oriantation of the cutting tool and restraining of the part.
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